Linewidth Single-frequency Research Articles

C + L-band tunable sub-kHz linewidth single frequency fiber laser by combining a fiber sub-ring with a saturable absorber

A sub-kHz linewidth single-frequency fiber laser that can be tuned in the full range of C + L band is proposed and experimentally demonstrated. A broad band gain fiber by bidirectional pumping combining with a wide tunable filter is used to realize 75.87 nm tuning range from 1529.98 to 1605.85 nm, which can be further improved if a wider tunable filter is available. To achieve single-frequency ultra-narrow linewidth laser operation, a ring-cavity laser configuration with a fiber sub-ring and a saturable absorber is utilized. The measured optical signal-to-noise ratio (OSNR) of the fiber laser is over 80 dB, the side mode suppression ratio (SMSR) can be improved to ∼60 dB, and the linewidth can be narrowed to ∼453 Hz. The output power of the laser exceeds 28 mW, and the slope efficiency is 2.05 %. This proposed fiber laser has the advantages of narrow linewidth, excellent wavelength tunability, and high output power, which is promising for the applications in optical sensing and optical communication systems.

A wavelength tunable single frequency microfiber laser

A wavelength tunable narrow linewidth microfiber laser is demonstrated. The oscillating emission of the microfiber laser is provided by a double-knot with a cavity length around 1.75 mm, which is fabricated by using a homemade Er3+/Yb3+ co-doped phosphate glass fiber. The diameters of the two knots are 206 and 351 μm respectively, while the diameter of the microfiber is about 1.88 μm. Based on this compact structure, a 2 kHz linewidth single frequency laser is realized with a wavelength tuning range larger than 18 nm. The side-mode-suppression ratio is higher than 38 dB, and the relative intensity noise (RIN) is measured to be −110 dB Hz−1 at frequencies of over 50 kHz.

Narrow linewidth single frequency microfiber laser

A compact 2 kHz linewidth single frequency microfiber ring laser is demonstrated. Microfiber, with a diameter of 1.88 μm, which is drawn from an Er(3+)/Yb(3+) co-doped phosphate glass fiber, serves as the gain medium. By using this microfiber, a double-knot resonator with a total length of 1.75 mm is constructed. Based on this resonator, a narrow linewidth single frequency laser with output power higher than 0.95 μW is obtained at the wavelength of 1536.1 nm. The linewidth of this microfiber laser is as narrow as 2 kHz, and the side-mode-suppression ratio is higher than 38 dB.